Banknotes and like securities are commonly produced by processing successive individual sheets or portions of a continuous web each carrying a plurality of individual imprints arranged in a matrix of rows and columns, which sheets or web portions are subjected to various printing and processing steps before being cut into individual documents (or notes). Amongst the printing and processing steps typically carried out during the production of banknotes are offset printing, intaglio printing, silk-screen printing, foil application, letterpress printing and varnishing. Other processing steps might be carried out during the production such as window cutting, ink-jet marking, laser marking, micro-perforation, etc. Once fully printed, the sheets or successive portions of continuous web have to be subjected to a so-called finishing process whereby the sheets or successive portions of continuous web are processed (i.e. cut and assembled) to form individual documents that are typically bundled and packed.
FIG. 1 summarizes a typical process of producing securities such as banknotes. The production process illustrated in FIG. 1 is advantageous in that it enables maximisation of the production efficiency by reducing waste to a minimum and enables the production of bundles and packs of bundles with uninterrupted numbering sequence.
Step S1 in FIG. 1 denotes the various printing phases which are typically carried out during the production of securities. As mentioned, these various printing phases include in particular an offset printing phase whereby sheets are printed on one or both sides with an offset background, an intaglio printing phase whereby the sheets are printed on one or both sides with intaglio features (i.e. embossed features which are readily recognizable by touch), a silk-screen printing phase whereby the sheets are printed on one or both sides with silk-screen features, such as features made of optically variable ink (OVI), and/or a foil/patch application phase whereby foils or patches, in particular so-called optically variable devices (OVD), holograms, or similar optically diffractive structures, are applied onto one or both sides of the sheets, etc.
As a result of the various printing phases of step S1, successive printed sheets 100 are produced. While quality control checks are usually performed at various stages during the production of the securities, a final quality check is typically carried out on the full sheets after these have completely been printed. This full-sheet quality inspection is schematised by step S2 in FIG. 1. Three categories of sheets in terms of quality requirements are generated as a result of this full-sheet quality inspection, namely (i) good sheets (i.e. sheets carrying securities which are all regarded to be satisfactory from the point of view of the quality requirements), (ii) partly defective sheets (i.e. sheets carrying both securities which are satisfactory from the point of view of the quality requirements and securities which are unacceptable, which defective securities are typically provided with a distinct cancellation mark), and (iii) entirely defective sheets carrying no acceptable security. From this point onward, the three categories of sheets follow distinct routes. More precisely, the entirely defective sheets are destroyed at step S10, while the good sheets are processed at steps S3 to S5 and the partly defective sheets are processed at steps S20 to S23.
Referring to steps S3 to S5, the good sheets are typically numbered at step S3, then optionally varnished at step S4, and finally cut and subjected to an ultimate finishing process at step S5, i.e. stacks of sheets 100 are cut into individual bundles of securities 200, which bundles 200 are typically banderoled (i.e. surrounded with a securing band) and then stacked to form packs of bundles 210. While the sheets 100 are processed in succession at steps S3 and S4, step S5 is usually carried out on stacks of hundred sheets each, thereby producing successive note bundles 200 of hundred securities each, which note bundles 200 are stacked to form, e.g., packs 210 of ten note bundles each.
Referring to steps S20 to S23, the partly defective sheets are firstly cut into individual securities at step S20 and the resulting securities are then sorted out at step S21 (based on the presence or absence of the cancellation mark previously applied at step S2 on the defective securities), the defective securities being destroyed at step S10, while the good securities are further processed at steps S22 and S23. At step S22, the individual securities are numbered in succession and subsequently subjected to a finishing process at step S23 which is similar to that carried out at step S5, i.e. note bundles of securities 200 are formed, which note bundles 200 are banderoled and then stacked to form packs of note bundles 210.
While FIG. 1 is discussed in the context of the production of securities on individual sheets, it shall be understood that the same principle is applicable to the production of securities on a continuous web. In that context, steps S1, S2, S3 and S4 could each be carried by processing a continuous web of printed material, which continuous web is ultimately cut into individual securities.
As regards the varnishing operation, FIG. 1 shows that such varnishing is typically carried out on full sheets at step S4 after full-sheet numbering at step S3. While this varnishing step is preferred, it is not as such required. Varnishing may furthermore be carried out at a different stage of the production, for example before or immediately after full-sheet inspection at step S2 (which other solution would imply that numbering is carried out after varnishing).
In case keeping the numbering sequence throughout the securities of successive bundles 200 is not required, the partly defective sheets could follow a somewhat similar route as the good sheets, i.e. be subjected to a full-sheet numbering step (thereby numbering both the good and defective securities), then to full-sheet varnishing, before being cut into individual securities, sorted out to extract and destroy the defective securities, and then subjected to an ultimate finishing process to form bundles and packs of bundles (in this case single-note numbering would not be required). Such an alternate production process is illustrated in FIG. 2A.
Step S1* in FIG. 2A is similar to step S1 of FIG. 1, i.e. successive sheets 100 are produced, i.e. subjected successively to offset printing, intaglio printing, silk-screen printing, foil/patch application, etc. Step S2* in FIG. 2A is similar to step S3 of FIG. 1, i.e. full sheets are numbered in an appropriate numbering press. In this case however, one shall understand that both good and defective sheets are numbered. The numbered sheets are then optionally varnished at step S3*, before being cut into individual notes at step S4*.
At step S5*, single-note inspection is carried out, i.e. each individual note is inspected from the point of view of quality, and defective notes are sorted out in the process, which defective notes are destroyed at step S7*. The good notes, on the other hand, are then subjected to an ultimate finishing operation at step S6*, i.e. individual note bundles 200 are formed, which note bundles 200 are stacked to form packs 210 of note bundles 200, e.g. packs of ten bundles.
According to a variant of the production process of FIG. 2A, numbering could be carried out in a single-note numbering process before or after the single-note inspection and sorting at step S5*. Such variant is illustrated in FIG. 2B. Steps S1**, S2**, S3**, S4**, S6** and S7** respectively correspond to steps S1*, S3*, S4*, S5*. S6* and S7* of FIG. 2A and do not need to be explained again. In the variant of FIG. 2B, as compared to the process of FIG. 2A, full-sheet numbering is replaced by a single-note numbering process (step S5**) following the single-note inspection and sorting at step S4**. In other words, the good notes sorted out after step S4** are numbered, preferably in a consecutive manner before being bundled and packed at step S6**.
For the sake of completeness, one may refer to International applications Nos. WO 01/85457 A1, WO 01/85586 A1, WO 2005/008605 A1, WO 2005/008606 A1, and WO 2005/104045 A2 for an overview of possible full-sheet quality inspection machines to carry out step S2 in FIG. 1. Of particular interest are the machines disclosed in International applications WO 01/85457 A1, WO 01/85586 A1, WO 2005/008605 A1 and WO 2005/008606 A1 which combine the functions of full-sheet quality inspection and full-sheet numbering (which machines can thus perform the operations of steps S2 and S3 in one pass). A full-sheet inspection machine is sold by the Applicant under the trade name Nota Check®, while a combined full-sheet inspection and numbering machine is sold by the Applicant under the trade name Super Check Numerota®.
The interested reader may furthermore refer to U.S. Pat. Nos. 3,939,621, 4,045,944, 4,453,707, 4,558,557, to European patent applications Nos. EP 0 656 309 A1, EP 1 607 355 A1, and to International applications Nos. WO 01/49464 A1, WO 2008/010125 A2/A3, all in the name of the present Applicant, for a discussion of various cutting and finishing machines suitable for carrying out step S5 of FIG. 1. Such machines are for instance sold by the Applicant under the trade name CutPak®. Those machines are easily adaptable to perform only cutting of sheets into individual notes at step S20 of FIG. 1, step S4* of FIG. 2A, or step S3** of FIG. 2B.
As regards the more specific issue of full-sheet numbering, European patent application No. EP 0 598 679 A1 and International application No. WO 2004/016433 A1 are of interest. The numbering and finishing principle discussed in WO 2004/016433 A1 is of particular interest in this context as it provides for the numbering of sheets in a manner such that bundles of securities are produced in a consecutive and uninterrupted numbering sequence at the end of the finishing process without this requiring any complex bundle collating system. Numbering machines for carrying out full-sheet numbering are for instance sold by the Applicant under the trade name SuperNumerota®, as well as under the above-mentioned Super Check Numerota® trade name.
In the context of single-note sorting and numbering as provided under steps S21 and S22 of FIG. 1, one may refer to U.S. Pat. Nos. 3,412,993, 4,299,325, 4,915,371. A machine combining the functions of single-note sorting and numbering (and optionally bundling and packing) is for instance sold by the Applicant under the trade name NotaNumber®. Such machine could for instance be used to carry out single-note sorting, numbering and finishing in the processes of FIG. 1 (steps S21 to S23) and FIG. 2B (steps S4** to S6**).
Single-note inspection and sorting systems for carrying out step S5* in the process of FIG. 2A and step S4** in the process of FIG. 2B are also known as such in the art.
As regards both production principles illustrated in FIGS. 2A and 2B, several single-note processing stations have to be installed in parallel in order to reach a comparable production efficiency as that of the production principle illustrated in FIG. 1, as this will be explained below.
A conventional production rate of a sheet-fed production line is of the order of 10,000 to 12,000 sheets per hour. The same applies to web-fed production lines. Depending on the sheet layout, such production rate typically corresponds to a note output of between 400,000 to 720,000 notes per hour (it being understood that each sheet typically carries between 40 to 60 notes). Single-note processing systems are limited by the natural laws of physics to a processing speed of approximately 120,000 notes per hour.
In the context of the production principle of FIG. 1, the above-mentioned limitations are not critical as a single-note processing system is only used at steps S21 and S22 to process partly defective sheets, which partly-defective sheets amount to only a small portion (e.g. <10%) of the production volume. In contrast, in the context of the production principles of FIGS. 2A and 2B, the whole production volume is processed at step S5* and S6*, respectively S4** to S6**, on a single-note processing system. In other words, in order to cope with the higher production rate of the sheet-fed production line, usually four or five single-note processing stations are used in practice to process the whole production volume in parallel. This will now be explained in reference to FIG. 3 which is also illustrative of the art and shows a possible implementation for carrying out the production principle of FIG. 2A.
In FIG. 3, reference 300 denotes a sheet-fed production line (or sheet-fed processing system), in this example with seven successive sheet-fed printing or processing stations 301 to 307, e.g. an offset printing press 301, a silk-screen printing press 302, a foil application machine 303, an intaglio printing press 304, a numbering press 305, an optional varnishing machine 306 and a cutting machine 307. Stations 301 to 304 perform full-sheet printing of unprinted sheets 100* according to step S1* of FIG. 2A, thereby yielding a set of printed sheets 100 which are numbered at station 305 and then varnished at station 306 before being cut into individual documents or notes 150 at station 307 (i.e. the sheets are processed in succession according to steps S2*, S3* and S4* of FIG. 2A).
As illustrated in FIG. 3, the sheet-fed processing system 300 is coupled to a single-note processing system 400 comprising a plurality of single-note processing stations SNPS 1 to SNPS 4 (also designated by reference numerals 401 to 404) which are coupled to the output of the sheet-printing and processing line 300 to process the individual documents 150 in order to produce bundles 200 and packs 210 of bundles 200 (each station 401 to 404 performing at least steps S5* and S6* of FIG. 2).
Let us consider for the sake of explanation that, in the context of FIG. 3, each printed sheet bears fifty notes, which means that the production capacity of the sheet-fed production line would be of 500,000 notes per hour at a sheet-processing speed of 10,000 sheets per hour. In this case, and considering a single-note processing speed of 120,000 notes per hour, four single-note processing systems are required to best match the production speed of the sheet-fed processing system 300, such being the case in the illustration of FIG. 3.
In order to implement the production principle of FIG. 2B, a similar production facility as that illustrated in FIG. 3 could be used. The only difference would reside in the fact that the numbering press 305 would be discarded and that each single-note processing station SNPS 1 to SNPS 4 would be provided with its own numbering capability to carry out the single-note numbering process of step S5** of FIG. 2B.
An improved solution for performing the production principle of FIG. 2A or 2B is discussed in International application No. WO 2008/126005 A1 in the name of the present Applicant.
Irrespective of the methodology that is adopted to process the printed sheets into individual documents, the sheets must undergo a finishing process where the sheets are stacked and cut to form individual documents as explained in connection with steps S5 and S20 of FIG. 1, step S4* of FIG. 2A or step S3** of FIG. 2B. This requires a suitable cutting and finishing machine for carrying out the cutting of the sheets in a precise manner.
As already mentioned, such cutting and finishing machines (as designated for instance by reference numeral 307 in FIG. 3) are already known in the art, for instance from U.S. Pat. Nos. 3,939,621, 4,045,944, 4,453,707, 4,558,557, European patent applications Nos. EP 0 656 309 A1, EP 1 607 355 A1, and International applications Nos. WO 01/49464 A1 and WO 2008/010125 A2/A3, all in the name of the present Applicant.
According to these known machines, the sheets are cut row-wise and column-wise while a predetermined number thereof (e.g. hundred) are stacked one upon the other. However, depending on the type of substrate used, the type and location of security features and various other process-related or design-related issues, stacking of the sheets may lead, as schematically illustrated in FIG. 5, to a substantial overall waviness ΔH of the sheet stacks, H designating the sheet stack height, while L and W respectively designate the sheet length and sheet width (see also FIG. 4). In particular, while the sheet at the bottom of the sheet stack may lie substantially flat, waviness increases as one moves to the upper sheets in the sheet stack. This waviness, which is not constant over the whole height of the sheet stack, can negatively affect the cutting accuracy row-wise and/or column-wise, possibly leading to cutting errors. In the schematic illustration of FIG. 5 where the waviness is particularly present along the X axis, this waviness can lead to cutting errors ΔX of the Y-cut, i.e. the cut along the Y axis. Moreover, since the waviness increases as one moves to the upper sheets in the sheet stack, the effective size of the documents cut row-wise and column-wise from the sheet stack will vary between the bottom sheet and the top sheet of the sheet stack, thereby leading to individual documents having varying sizes, which is not desired.
An improved solution for processing printed sheets into individual documents is therefore required.